An important area of research in cognitive development is the ability to recognize and infer the mental states of others. This ability is ubiquitous in our social lives; however; we do not appear to have sophisticated attributional abilities until around the age of 4- or 5-years. Despite two decades of research on mental retardation, it remains unclear where these skills come from, how they are acquired, and how they work. Investigating the extent of infants' reasoning about he minds of others will not only further define the developmental progression of such abilities but will also allow for an analysis of the abilities that are available prior to the development of formal language skills, speak to ongoing discussion regarding the innateness of some attributional mechanisms, and characterize the extents, limits, and input requirements of these mechanisms. The proposed research will investigate the ability of infants to make mental state attributions. Aim 1 will examine the extents and limits of infants' understanding of intentionality. Aim 2 will examine the cues that are important to making mental attributions of intentionality. Finally, Aim 3 will examine how infants interpret failed intentions.